Environmental Life Cycle Assessment of Silage Maize in Relation to Regenerative Agriculture

Agriculture is among the most significant drivers of changes in the environment [1] and has a major impact as 40% of the global ice-free land area is already under agriculture [2]. Agriculture contributes approximately 9.8% of total greenhouse gas emissions of carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) in European Union (EU) countries [3]. These three main gaseous emissions contribute approximately 80% of the greenhouse effect [4] and therefore contribute greatly towards climate change [5]. This can further impact the soil [6], water bodies [4], air quality, and human health [7]. The environmental impact of crop production systems is usually related to the use of fossil fuels [8], emissions generated from the use and application of mineral and organic fertilizers [8,9], and the production of fertilizers [10]. Agriculture has a significant environmental footprint [11]. Food production is associated with more than 5% of global greenhouse gas emissions [12]. Hence sustainable agricultural practices can play a huge role in reducing the overall impact of agriculture on the environment.

One of the ways to ensure sustainable food production is so-called regenerative agriculture. Regenerative agriculture is a completely new term in the Czech Republic, which the agricultural and academic public was introduced to for the first time in 2021. Regenerative agriculture aims to maintain agricultural productivity, increase biodiversity, and in particular restore and maintain soil biodiversity, and enhance ecosystem services including carbon capture and storage. Regenerative agriculture is based on farming without tillage, and without the use of fertilizers and pesticides. Moreover, according to [13] “regenerative agriculture has at its core the intention to improve the health of soil or to restore highly degraded soil, which symbiotically enhances the quality of water, vegetation, and land-productivity”. The first visions of sustainable agriculture appeared as early as the 1980s [14] and pressure for sustainable food production continues to grow [15]. According to [16] the concept of generative agriculture has seen a rapid increase in farming, popular, and corporate interest, the scope of which now sees regenerative agriculture best viewed as a movement. [17] noted the growing interest in regenerative agriculture among several actors in the public, private, and non-profit sectors, as well as in academia.

Maize (Zea mays L.) is among the world’s leading grown cereal crops [18] and is the third most important export product of Czech agriculture after wheat and barley [19]. In the Czech Republic is maize mainly grown for silage and corn grain production [20]. According to the ČSU [21], the total area of silage maize grown in the Czech Republic amounted to 212 thousand ha. Maize is not only an important staple crop for millions of people worldwide but also an important crop now emerging as a type of high-energy silage crop [21], used to produce animal feed due to its high feeding value [22]. The corn crop provides an excellent combination of high dry-matter yield per hectare and the quality of the biomass produced [23]. Silage corn is an important crop for the Czech Republic also as a crop for energy use in biogas stations.

The increase in crop yields in modern agriculture has been increasingly dependent on inputs of Fertilizers and pesticides [24]. Most common mineral fertilizers require large quantities, typically 80–140 kg per hectare of land [25]. This widespread usage in agricultural systems has multiple impacts on the environment [26]. Only 30–50% of the amount of nitrogen (N) and phosphorus (P) fertilizers applied is utilized by the crop [27]. Excessive applications of N and P to cropland accumulate in agricultural soils and are subsequently lost to surface and groundwaters by leaching and erosion [28]. The loss of these nutrients in agricultural fields is a cause of environmental pollution [29,30]. The disadvantages include possible biomagnification and persistence in nature [31]. The application of P, K, and S fertilizer increases the N efficiency and helps achieve higher yields with higher protein [32]. Rational, balanced organo-mineral fertilization is necessary to produce sufficient quantities (food security) of high-quality food (food safety), with minimal impact on the environment [33,34]. Agriculture must find the right compromises between current and future levels of production by effectively using fertilizers to avoid excessive emissions to the environment [35].

The sustainable development of agriculture is currently facing challenges from climate change, as well as soil pollution and degradation resulting from intensive farming practices [36]. Conventional approaches to intensify agriculture and the use of fertilizers and pesticides are among the major causes of environmental degradation [37]. It is widely recognized that mineral fertilizers have made a significant contribution to the continuous increase in agricultural food production in the past decades [38]. However, the increased application intensity, especially when overused, also brings a series of environmental burdens [39]. Mineral fertilizers and plant chemical protection are important for crop output, but they can also emit specific quantities of emissions and cause environmental burdens [40,41]. Pesticides from agricultural fields are often found in waterbodies leading to environmental effects [42]. This can have an impact on water pollution and aquatic biodiversity [43].

Increasing concerns about environmental impacts and reductions of inputs require a transformation of cropping systems for improved efficiency and sustainability. Achieving this goal with limited environmental impacts offers an unprecedented challenge to humankind [44]. Thus, it is necessary for the continued establishment of ways to assess and promote agricultural practices that can be adopted by farmers, which present a more environmentally sustainable and friendly. Thanks to life cycle assessment (LCA), it is possible to assess the environmental impact of agricultural systems. The LCA method is a comprehensive tool that enables the assessment of various environmental impacts directly caused by the farming system and the impacts arising from the inputs [9]. Comparative LCA studies can help find suitable alternative or mitigation strategies in crop production [40]. The LCA is a standard method used to assess the environmental impacts and to evaluate the sustainability of the production systems from the environmental point of view [45] by quantifying the energy, material flows, and environmental releases and converting them to environmental impacts [46], which allows for the identification of life cycle stages that contribute disproportionately to specific areas of environmental concern.

There have been many LCA studies conducted on maize production globally [8,41,42,43,44,45,46,47]. In conditions of the Czech Republic there have been advancements in LCA studies regarding maize production e.g., ref. [48] assessed the environmental potential Szarvasi-1 as a substitute energy crop of maize, while ref. [49] evaluated maize performance relating to climate change impact category and ref. [50] evaluate cup plant as an alternative to silage maize. There hasn’t so far been an LCA study of silage maize comparing different mineral fertilizer and pesticide dose applications in the Czech Republic regarding regenerative agriculture. This is an important approach towards achieving the EU Green Deal policy emissions target by 2050 [51].

The goal of this study was to quantify (a) the environmental impacts of different mineral fertilizer and pesticide dose applications and (b) the impact of different mineral fertilizer and pesticide doses on yield within the framework of determining emission limits in silage maize production. The achieved results are useful for promoting the overall reduction of environmental impact by optimizing mineral fertilizer and pesticide doses. The system boundaries define the life cycle processes that belong to the analyzed system [52]. For this study system boundaries were all processes from “cradle to farm gate” which includes all inputs, upstream processes, and outputs as shown in Figure 1. The functional unit chosen for this study was 1 ton of final product and the mass allocation principle was employed. The functional unit determines the nature of the study outputs and their interpretation is one of the key moments in implementing the LCA study [53,54,55] and is a quantitative description of the function of the system. The transport distance between the field and the farm site was estimated to be 5 km. This study was conducted according to the guidelines of the International Organization for Standardization [56,57].

Global agriculture productivity continues to face several abiotic and biotic challenges. The results obtained show that the different fertilizer and pesticide doses applied had a significant impact on the environment. Considering the impact agriculture continues to have on the environment, it is necessary for the continued assessment of production systems using the LCA method. The LCA quantifies the energy, material flows, and environmental releases and converts them to environmental impacts [47].

Global warming, as recognized by the United Nations, is a key factor contributing to climate change [63]. According to the results for the impact category the global warming, the highest environmental impact was associated with the variant M5 that had full dose input of N 160 kg ha ⁻¹ fertilizers (1247 kg CO_2eq) respectively. The higher environmental load can be attributed to the high doses of fertilizer application. The application of fertilizers had an influence on increased yields compared to the M1 variant that was not fertilized. While fertilizer has been observed to increase crop yield, it is also associated with environmental impacts. Several studies have attributed a higher environmental burden to high doses of mineral fertilizers [64,65]. N loss from fertilizers has become a persistent environmental problem [66]. The low nitrogen efficiency of maize implies that a substantial portion of applied fertilizers are not absorbed by plants and can escape nutrient pollution [67]. Nitrogen fertilizer can convert into nitrous oxide (N₂O) [68] which is an important greenhouse gas that contributes to global warming [69] and has a global warming potential (GWP) 265 times higher than CO₂ [70]. Nitrous oxide is produced during nitrification, resulting from microbial soil processes of converting ammonia (NH₃) to nitrate (NO₃−) and denitrification in the conversion of NO₃− to N₂. Yadav [71] observed that the agriculture sector can play a critical role in GHG mitigation by lowering 10% N₂O emissions. The reduction in N fertilizer doses can be saved as a mitigating strategy to reduce the impact of maize production contribution as shown in the results. Similar studies have attributed high GHG emissions to the use and application of N fertilizers [70,72].

According to the results for the impact category global warming, there was a significant difference in environmental load for the variant M2 (873.450 kg CO_2eq) and M4 (878.209 kg CO_2eq) that received a half dose of N 80 kg ha ⁻¹, fertilizers compared to the variants with full dose application of N 160 kg ha⁻¹ respectively M3 and M5. The control variant M1 with no input of N fertilizer had the lowest environmental impact for the impact category climate change. To decrease environmental impact and obtain an environmentally friendly production system [73], the reduction of nitrogen fertilizer use represents one of the most effective climate change mitigation strategies farmers can adopt [74], although this can be achieved at the cost of lower yield. The N application based on crop demands could be proposed to provide maximum uptake and consequently decrease NOx emissions through a decrease of NH₃ volatilization to reduce global warming potential [73]. Partial replacement of mineral N with organic fertilization can solve as a mitigation strategy as it not only provides NPK and micronutrients to the soil and crop but also organic C when using solid fertilizers [75] or utilizing nitrogen-fixing plants in a crop rotation can be a good way to avoid the overuse of nitrogen in the production system [38]. The other contributing factor to global warming was the burning of fossil fuels during agrotechnical operations (including tillage, sowing, fertilizing, cultivating, harvesting, and transporting). Tillage practices influence crop productivity but also influence GHG emissions [76]. No-till, reduced tillage systems, and combining operations can save and mitigate strategies to reduce the environmental contributions arising from the burning of fossil fuels [77]. The combustion of fossil fuel is considered responsible for more than 75% of human-caused CO₂ emissions [74]. Effective energy management is crucial for reducing GHG emissions [30]. Overall, according to the results the lowest environmental load for impact category global warming was associated with the control variant M1, and this is attributed to the non-use and application of fertilizers.

Global P and N consumption is increasing steadily due to the growing population and increased demand for food crops and animal-derived food [78]. According to the results for impact categories marine eutrophication and freshwater eutrophication the high environmental loads were associated with the variants that had full dose input of N 160 kg ha⁻¹ and P 30 kg ha⁻¹, respectively, M3 and M5. This is attributed to the large amounts of P and N fertilizers, and this is supported by the findings of Smith et al. [13] and Withers et al. [79]. The increased fertilizers use required for agricultural intensification has greatly increased the leaching of N and P to water surfaces [80]. Not all P and N fertilizers applied to agricultural land are taken up by plants or retained in the soil [60]. The Emissions created by applying fertilizer to crops included losses of total N, NO₃⁻-N, NH₄⁺-N, soluble phosphate, and total P, through runoff leaching resulting in eutrophication [71]. Eutrophication leads to reduced water quality, alteration of food web structures, loss of biodiversity, and habitat degradation [81]. The protection of water bodies requires the identification and quantification of contributing sources to find mitigating strategies. The variants with the dose of N 80 kg ha⁻¹ and P 15 kg ha⁻¹ recorded lower environmental burdens compared to the variants that received doses of N 160 kg ha⁻¹ and P 30 kg ha⁻¹. Hence the reduction of anthropogenic nutrient input in the agricultural systems remains key to reducing eutrophication. The results show that for the impact categories freshwater eutrophication (0.071 kg P_eq) and marine eutrophication (1.292 kg N_eq), the M1 variant had the lowest environmental impact.

According to the results for impact categories marine ecotoxicity and freshwater ecotoxicity the variant M3 with the full dose of N 160 kg ha⁻¹, P 30 kg ha^−1, and K 120 kg ha⁻¹ fertilizers and 1.3 L/mL Maister power pesticide. The process of increasing crop production utilizes the application of higher quantities of agrochemicals [82]. Pesticides are used in agriculture to protect crops from insects, weeds, and bacterial or fungal diseases during growth [65] and increase yield [64], but are associated with negative environmental impacts [83,84] and have become an issue globally [64]. The pesticides originating from human activity or agricultural farming are discharged directly or indirectly into the receiving water [85]. Pesticides and their effects on the ecosystems are still too often omitted in most LCA studies even though they are one of the major environmental issues linked with agriculture [86]. For impact category terrestrial ecotoxicity the high impact was associated with the variants that received full doses of pesticides, respectively, M3 and M4 which could disturb all biosphere’s constituents and may present a serious risk to human health and its environment [87].

According to the results, a reduction in the amount of pesticide dose application can be a mitigating strategy to reduce the effect of pesticides on the environment. Reducing pesticide use has become a shared goal by several countries and a major issue in public policies [88]. To achieve the Green Deal Goal of the EU of reducing mineral fertilizers and pesticide use by 50% by 2030 [51], a shift towards alternative cropping systems that are less dependent on pesticides is needed [89].